1. Field of the Invention
The present invention relates generally to the cooling of electronic systems having heat-dissipating components such as processors and, more particularly, to fan rotor systems having collapsible fan blades.
2. Related Art
Electronic systems typically include CPUs, CECs (generally, processors) and other heat-dissipating components. Such systems require a fan that pushes air through the system and/or over the components in order to keep the heat-dissipating components from overheating. Electronic systems have become more densely packaged and designing electronic systems within power and heat dissipation budgets have become more difficult. This evolution has posed a number of design challenges with respect to fan power consumption and the effect of fans on the heat dissipation characteristics of the overall system.
As an example of such densely packaged electronic systems, advances in the miniaturization of computer, communication and other electronic equipment have led to the development of so-called “blade” systems, which permit several circuit boards (“blades”) to be installed in a single chassis. The chassis typically includes components, such as power supplies, cooling fans, a blade manager and other components that are shared by the blades installed in the chassis. The blades typically plug into a backplane of the chassis, which distributes power and data signals between the blades, blade manager and other components. This arrangement enables a large number of blades to be housed in a relatively small chassis. Oftentimes, the chassis dimensions enable it to be mounted in a rack, such as a server rack with other rack-mounted equipment.
Blades can perform various functions. Most blades contain entire computers, including single or multiple processors, memory, and network interfaces. Oftentimes, computer blades are used as servers while others are used as communication devices, such as routers, firewalls or switches. Some blades contain specialized hardware components, in addition to or instead of general-purpose processors, memory, etc. In general, blades include any number of heat-dissipating components.
Some server blades include disk drives. Other blades access disk drives that are located elsewhere in the chassis or are connected to the chassis by computer network hardware. Typically, any type of blade can be plugged into any slot of a chassis. This enables an operator or system manager to combine blades in a chassis so that requisite operations can be performed by the blade system. In addition, the mixture of blade types can be changed to accommodate changes in operational requirements. For example, a system operator might choose to logically connect a blade to different disk drives to execute different application programs at different times of a day. In another example, if a blade fails, logical connections from off-blade disk drives that were formerly used by the failed blade can be redirected to a replacement or hot standby blade.
As noted above, while densely packaged electronic systems such as blade systems provide many advantages, several engineering challenges arise when using them. Among these challenges is the challenge of designing and operating a bladed system such that sufficient heat is dissipated in the limited space available in the chassis that hosts the system. Some known power limiting strategies include powering down a CPU functional unit, e.g., a floating point unit or an on-die cache, or reducing speed to attain reduced power consumption in a hard drive. To address heat dissipation challenges, bladed server systems can be designed with an underlying power and thermal envelope. For example, when a chassis that hosts a bladed system has a limited amount of airflow available to cool the blades (i.e., when the system can only dissipate a limited amount of heat), then the chassis is designed for a limited amount of power consumption and an associated limited performance of the blades.
As a result of the modularity, flexibility, and requirements of bladed and other densely packaged electronic systems, however, the systems, and also different portions or zones within the systems will require multiple fans to cool the electronics. Examples of such a multiple fan arrangement include multiple redundant fans within a single fan system package, as well as push-pull fan arrangements with one or more fans provided on a cooling air intake portion of an electronic system or zone within an electronic system and one or more fans provided on a cooling air output portion, or other combinations of multiple fans provided in series along a cooling zone. While the provision of such fans can provide some level of cooling, if one or more fans in the series of cooling fans should fail for any reason (such as, mechanical or electrical failure, power failure or shutdown due to exceeding system power budget, physical obstruction of the fan rotor, etc,), the failed fan creates a drag on the cooling air flowing therethrough. This can result in increased demand on other fans, overheating of the electronics, and/or scaling back of the performance of the electronics to prevent overheating.